This invention relates to a method and apparatus for continuously monitoring the internal structure of metal strip subjected to an annealing treatment. In particular, it relates to the continuous, contactless monitoring of the grain structure of cold metal strip to determine the effect of annealing. The monitoring is done by means of a measuring arrangement consisting of at least one magnetic flux-producing device and a measuring sensor immediately associated therewith to determine energy loss.
Continuous, contactless monitoring of the internal structure of an elongated magnetizable material, preferably after heat treatment, is described in DE-AS Nos. 20 50 827 and 20 65 826. In order to judge the internal structure, an apparent remanence is used as the measuring variable which represents a measure of the coercivity. The coercivity reaches a minimum if the strip is completely recrystallized by an annealing treatment. The measuring arrangement comprises a magnetizing device that includes cylindrical permanent magents and a measuring sensor separated by a certain distance from the magnetizing device and containing a Hall probe. The strip travels through a measuring path past the magnetizing device and the measuring sensor, and the Hall voltage generated by the measuring sensor is evaluated and recorded as a measure of the apparent remanence.
One disadvantage of that method is that the measuring apparatus is sensitive to changes in the distance between the strip, the measuring device, and the measuring sensor as well as to shock and vibration, and is influenced by remanent external fields. The prior art methods are also limited to measuring strips of ferromagnetic material.